The PI wishes to learn how the pineal gland functions in the regulation of circadian rhythms in vertebrates. To this end, melatonin synthetic rhythms will be studied in the eyes and pineal glands of developing rats and chicks. The PI recently identified the eye as a nonpineal site of rhythmic melatonin synthesis -- detailed studies of the regulation of ocular melatonin production by light and dark will be undertaken. Developing rats have been found by Mildred Brammer and the PI to have pineal glands that are capable of intrinsic rhythms and possibly, light perception. These abilities will be defined and the role of sympathetic innervation as a possible cause of loss of these abilities will be investigated. The requirement for vitamin A will be determined. An attempt will be made to obtain long-term (more than two cycles) persistence of pineal rhythmicity in vitro to enhance utility of the system in determining the mechanism for circadian rhythm generation.